High performance formulated lubricants depend heavily on the performance characteristics of component base oils (or basestocks) used in blending such products. One traditional problem regarding lubricant oil performance is that of achieving a useable balance of both low-temperature and high-temperature properties. For example, modern multigrade engine oils demand significant performance both at low temperature (for cold engine starts and oil pumpability) as well as at high temperature (viscosity retention, resistance to oxidation and thermal degradation). The trend to SAE “0W” grade engine oils, for example, which require superior low temperature flow properties, increases the demand for lubricants having improved combination of low-temperature and high-temperature performance.
Indeed, the viscosity-temperature relationship of the oil is one of the critical criteria which must be considered when selecting a lubricant for a particular application. For example, the viscosity requirements for qualifications as multi-grade engine oils are described by the SAE Engine Oil Viscosity Classification-SAE J300. These standards apply to both passenger care engine oils (PCEO) and commercial engine oils (CEO). The high-temperature (100° C.) viscosity is measured according to ASTM D445, Method of Test for Kinematic Viscosity of Transparent and Opaque Liquids, and the results are reported in centistokes (cSt). The HTHS viscosity, or high-temperature (150° C.) high-shear (106 s−1) viscosity, is measured according to ASTM D4683, Test Method for Measuring Viscosity at High Temperature and High Shear Rate by Tapered Bearing Simulator, and the results are reported in centipoise (cP). The low-temperature (W) viscosity requirements are determined by ASTM D 5293, Method of Test for Apparent Viscosity of Motor Oils at Low Temperature Using the Cold Cranking Simulator (CCS), and the results are reported in centipoise (cP). A second low-temperature viscosity requirement, simulating low-temperature pumping conditions, is determined by MRV (mini rotary viscometer), ASTM D4684, Method for Determination of Yield Stress and Apparent Viscosity of Engine Oils at Low Temperature, with yield stress reported in pascals (Pa) and viscosity reported in centipoise (cP). In addition, a low-temperature pumpability requirement is imposed on multigrade oils, as determined by MRV. It should be noted that CCS viscosity (measured under high energy, high shear conditions) and MRV viscosity (measured under low energy, low shear conditions) are different low-temperature physical properties of lube base oils, and each measures a different characteristic of lube waxiness. Formulated passenger car engine oils must simultaneously meet both critical low-temperature properties of CCS viscosity and MRV viscosity. Table 1 (below) outlines the high- and low-temperature requirements for the recognized SAE grades for engine oils.
TABLE 1Engine Oil Viscosity Grade Specifications (SAE J300)High-Temperature ViscositiesKinematicLow-Temperature ViscositiesViscosityCCSMRVat 100° C.HTHSSAEViscosityViscosity(cSt)ViscosityGrade(cP)(cP)MinMax.(cP) 0 W3250 at −30° C.60000 at −40° C.3.8 5 W3500 at −25° C.60000 at −35° C.3.810 W3500 at −20° C.60000 at −30° C.4.115 W3500 at −15° C.60000 at −25° C.5.620 W4500 at −10° C.60000 at −20° C.5.625 W6000 at −5° C. 60000 at −15° C.9.3205.6<9.32.6 min309.3<12.52.9 min4012.5<16.32.9 min(PCEO)4012.5<16.33.7 min(CEO)5016.3<21.93.7 min6021.9<26.13.7 min
The SAE J300 viscosity grades as well as viscosity grades reaching lower or higher than those defined by SAE J300 are encompassed by this specification.
In a similar manner, SAE J306c describes the viscometric qualifications for axle and manual transmission lubricants. High temperature (100° C.) viscosity measurements are performed according to ASTM D445. The low temperature viscosity values are determined according to ASTM D2983, Method of Test for Apparent Viscosity at Low Temperature Using the Brookfield Viscometer and these results are reported in centipoise (cP). Table 2 summarizes the high- and low-temperature requirements for qualification of axle and manual transmission lubricants.
TABLE 2Axle/Transmission Oil Viscosity SpecificationsKinematicViscositySAEMaximum Temperatureat 100° C.Viscosityfor Viscosity of(cSt)Grade150,000 cP (° C.)MinMax 70 W−55— 75 W−404.1 80 W−267.0 85 W−1211.0 90—13.524.0140—24.041.0250—
In addition to the viscosity temperature relationship, other properties are, of course, required for an engine oil including, but not limited to, resistance to oxidation under the high temperatures encountered in the engine, resistance to hydrolysis in the presence of the water produced as a combustion product (which may enter the lubricating circulation system as a result of ring blow-by), and since the finished oil is a combination of basestock together with additives, these properties should inhere in all of the components of the oil so that the final, finished lubricant possesses the desired balance of properties over its useful life.
High performance lubricant products with the desired range of low-temperature and high-temperature performance properties may be achieved by formulating with synthetic base oils, including polyalphaolefins (PAO). Synthetic base oils such as PAO are highly advantageous in formulating high-performance lubricants, with desirable low-temperature and high-temperature performance properties. In particular, PAO have especially exhibited excellent low-temperature performance due to its chemical structure and to a composition which contains no waxy hydrocarbon components. One problem with PAO fluids, however, is that they are generally resistant to easy biodegradation due to their chemical structure. In the event of a release, lubricating oils, including engine oils, gear oils, and transmission oils, may persist long enough to disturb the natural state of the environment. Having high rates of biodegradation is advantageous in the event of such a lubricant release into the environment.
Finished lubricants may also be formulated with high-quality hydroprocessed base oils. Hydroprocessed base oils, however, have traditionally demonstrated poorer low-temperature properties and performance than synthetic base oils such as PAO. Accordingly, lube products formulated with hydroprocessed base oils have had problems in achieving the low-temperature performance of lube products formulated with PAO base oils. On the other hand, certain hydroprocessed base oils have demonstrated good biodegradability, especially when compared to that of synthetic base oils like PAO.
WO 97/21788 discloses biodegradable hydroprocessed base oils with pour points of −15° C. to −24° C., with 6.0–7.5 methyl branches per 100 carbons for a hydrocarbon fraction with a boiling point above 700° F., and with 6.8–7.8 methyl branches per 100 carbons for a typical 100N base oil.
U.S. Pat. No. 5,366,658 discloses biodegradable base oils for lubricants and functional fluids comprising polymethylalkanes, having terminal methyl groups and having methylene and ethylidene groups. Because of the highly specific synthesis schemes used in making these polymeric fluids, the structure of the polymethylalkanes is highly constrained with branches along the hydrocarbon polymer backbone being exclusively single-carbon (C1) methyl groups. This structure type is different from that possessed by the wax isomerate fluids, in which the branching groups along the long-chain hydrocarbon backbone include not only methyl (C1) but also ethyl (C2), propyl (C3), butyl (C4), and possibly other longer hydrocarbon groups. Such mixtures of branching groups, with differing chain lengths/sizes, impart performance characteristics to long-chain hydrocarbons that are different from the performance features imparted by only methyl (C1) branches.
U.S. Pat. No. 5,595,966 and EP 0468109A1 both disclose substantially biodegradable hydrogenated polyalphaolefin (PAO) fluids, which demonstrate from 20% and to at least 40% biodegradation in the CEC L-33-T-82 test. EP 0558835A1 discloses substantially biodegradable unhydrogenated PAO fluids, which demonstrate from 20% to at least 50% biodegradation in the CEC L-33-T-82 test. The PAO's of these references have a chemical structure consisting of a short-to-moderate chain length hydrocarbon backbone with only a few long-chain pendant groups attached.
Normally, a finished lubricant will contain several lubricant components, both base oil(s) and performance additive(s), in order, for example, to achieve desired performance requirements. The development of a balanced lubricant formulation involves considerably more work than the casual use of performance additive(s) in combination with base oil(s). Quite often, functional difficulties may arise from combinations of these materials with certain base oils during actual operating conditions, and unpredictable antagonistic or synergistic effects may become evident. Thus, obtaining suitable formulations require extensive testing and experimentation. Likewise, subtle features of a base oil's chemical composition may significantly influence a base oil's performance in a formulated lubricant. Therefore, matching base oil technology with additive technology is not a routine exercise.
It has now been discovered that certain wax-isomerate basestocks of the present invention demonstrate unusually good low-temperature and high-temperature properties which allow unusually broad formulation flexibility compared to traditional hydroprocessed base oils. For example, these formulated wax-isomerate type lubricants can meet the extremely stringent viscosity requirements of SAE “0W”, particularly SAE 0W-40 crossgraded engine oils, whereas typical hydroprocessed oils with compositions outside the defined compositional range of the present invention cannot reach such a wide crossgrade. Achieving SAE “0W-XX” crossgrades (e.g. XX=20, 30, 40, 50, 60) is of particular utility because such lubricant formulations are known to have improved fuel economy performance over comparable 5W-XX and higher “W” viscosity grades. Such formulation flexibility at both low and high temperatures is typical of premium synthetic PAO basestocks. In addition, the wax-isomerate derived base oils of this invention unexpectedly demonstrate very good biodegradability, especially when compared to PAO base oils.